Ophiuchus, Serpens
O
phiuchus is another large constellation, covering
948 square degrees of the sky, but it is confusingly
intertwined with the two parts of Serpens. It straddles the
equator; of its brighter stars Îis at declination 9 degrees
north, ıalmost 25 degrees south. There is no distinctive
pattern, and the only star bright enough to be really
prominent is ·(Rasalhague), which is 62 light-years away
and 67 times as luminous as the Sun. Rasalhague is much
closer and less powerful than its neighbour Rasalgethi, in
Hercules (see Star Map 9), even though it looks a full
magnitude the brighter of the two. It is also different in
colour; Rasalhague is white, while Rasalgethi (·Hercules)
is a red supergiant.
Of the other leaders of Ophiuchus, ‰is of type M, and
its redness contrasts well with that of the nearby Â, which
is only slightly yellowish. The two are not genuine neigh-
bours; ‰is 140 light-years away, Âonly just over 100. It is
worth looking at them with binoculars, because they are in
the same field.
On the very edge of the constellation close to ÛScorpii
(one of the two stars flanking Antares) is a wide double
Ú Ophiuchi (not shown on map) which lies close
to a very rich region which is a favourite photographic
target. Ëis a binary with components which are not very
unequal (the primary is no more than half a magnitude
brighter than the secondary), but the separation is less than
one second of arc, so that it is a good test for telescopes of
around 25-centimetre (10-inch) aperture.The most interesting variable in Ophiuchus is RS,
which is a recurrent nova and the only member of the
class, apart from the ‘Blaze Star’, T Coronae, which can
flare up to naked-eye visibility – as it did in 1898, 1933,
1958, 1967 and 1987; the usual magnitude is rather below- It is at least 3000 light-years away, and is worth
monitoring, as a new outburst may occur at any time.
Ophiuchus was the site of the last galactic supernova,
Kepler’s Star of 1604, which for a while outshone Mars
and Jupiter. It is a pity that it appeared before telescopes
came into common use.
Another interesting object in the constellation is
Munich 15040, better known as Barnard’s Star because it
was discovered, in 1916, by the American astronomer
Edward Emerson Barnard. It is not easy to locate, because
its magnitude is below 9. It is the closest of all stars apart
from the members of the ·Centauri system, and has
the greatest proper motion known, so that in fact in only
190 years or so it will shift against its background by a
distance equal to the apparent diameter of the full moon.
It is an extremely feeble red dwarf, and irregularities in its
motion have led to the belief that it is attended by at least
one companion which is of planetary rather than stellar
mass, though definite proof is still lacking. The guide star
to it is 66 Ophiuchi, magnitude 4.6. Incidentally, this was
the region where an astronomer named Poczobut, in 1777,
tried to introduce a new constellation, Taurus Poniatowski,
or Poniatowski’s Bull; it also included 70 Ophiuchi (a
well-known but rather close binary), together with 67 and - Not surprisingly, the little Bull has been deleted from
current maps.
Ophiuchus contains no less than seven globular clus-
ters in Messier’s list. All of them are reasonably bright, so
that they are favourite objects for users of binoculars or
wide-field telescopes. M2 is interesting because it is less
condensed than most globulars, and is therefore easier to
resolve; it may be compared with its neighbour M10,
which is much more concentrated.
Mythologically, Ophiuchus is identified with
Aesculapius, son of Apollo and Coronis, whose skill in
ATLAS OF THE UNIVERSE
These constellations
are relatively hard to identify,
particularly as they are so
confused. In mythology
Ophiuchus was the Serpent-
bearer (a former name for
it was Serpentarius) and
Serpens was the reptile with
which he was struggling –
and which he has apparently
pulled in half! The only
bright star in the region is
·Ophiuchi (Rasalhague).
Ophiuchus extends into the
Zodiac between Scorpius
and Sagittarius, so that
the major planets can
pass through it. The globular cluster M12
in Ophiuchus, photographed
by John Fletcher using a
25-cm (10-inch) reflector.
M12 is easier to resolve
into individual stars than
other globular clusters
such as M10.MagnitudesVariable starGalaxyPlanetary nebulaGaseous nebulaGlobular clusterOpen cluster–1
0 1 2 3 4 5HERCULES
SCUTUM
OPHIUCHUS
SERPENS
CAUDASERPENS CAPUT
LIBRA
SCORPIUS
LUPUSAntares··ÎÈ
72‚ Û
Á67
6870ıËÓÍÓ‚·ÁÏ ‰ Â ̆ ̇ Ê ̄ËÍı45È
ÎÁ ‚
̄ ‰ Ï · Â ˆ Ì
RURSX
IC4665M14
M10
M12
M16
M107
M9
M5
M19
M62
Ô
SAGITTARIUS
AQUILA
CORONA
ÁÌ
Ï
‰Â ̇
ı
‚
·
‰ Á‚
Á‚·Á‚ ȉÛ
·
ÙÛ
ÚÂ Â Í ̄̇ ‰ ÁÙÛ
ÊÍ
ÔÏ̇Â66ˆGa Atl of Univ Phil'03stp 2/4/03 7:37 pm Page 236